French patent applications FR-A-2 749 489 and FR-A-2 749 490 disclose brushes that have a non-rectilinear core, e.g. that is shaped to match the curve of the eye. Such brushes are not suitable for all users, since the curve of the brush requires the user to perform strokes that certain people find difficult.
Patent application EP-A2-1 236 420 discloses a brush having a core that is curved over at least a fraction of its length, the free end of the brush not being in alignment with the axis of the stem. During manufacture of the device comprising the receptacle and the brush, such a brush can turn out to be relatively difficult to insert in the neck of the receptacle containing the composition.
European patent application EP-A-1 424 024 discloses an applicator comprising a brush having a core that includes a portion carrying the bristles that forms a non-zero angle of less than 20° with the longitudinal axis of the end of the stem.
Such brushes require the user to adapt the strokes they use, since said brushes do not enable the user to comb the eyelashes or the eyebrows in the same manner as with a conventional brush that has a core that does not slope relative to the longitudinal axis of the stem.
Brushes are also known that comprise a rectilinear core that extends along the axis of the stem and that has bristles that define an envelope surface that presents at least one concave or convex face.
French patent application FR-A-2 811 525 discloses “off-center” brushes having a core that extends in alignment with the stem and along the longitudinal axis of said stem, the brush presenting faces forming a non-zero angle with the longitudinal axis of the core.
The off-center brushes present the drawback of external appearance that can turn out to be disconcerting to the user. In addition, they are not wiped symmetrically from one end of the brush to the other, thereby causing flattening over continued use.